This invention relates to magneto-optic modulators of the bounce-cavity type.
A Nd:YAG fiber laser can operate at wavelengths of about 1.3 micrometers. At this wavelength fiber waveguides can be made that have both low loss and low dispersion. Unfortunately, due to the long fluorescent lifetime of the YAG crystal, high speed modulation of the output from this laser cannot be achieved by direct modulation of the pump diode current. Hence the Nd:YAG fiber laser requires an external modulator.
One type of magneto-optic modulator which can be utilized with a Nd:YAG fiber laser can be fabricated from garnet crystals. The magnetic garnets exhibit very high absorption at wavelengths shorter than 1.1 micrometers, but they can be made relatively transparent in the wavelength range of interest for fiber guide transmission from 1.1 micrometers to 1.5 micrometers, and they have an adequate figure of merit. Moreover, for magneto-optic devices, the drive power is proportional to the wavelength .lambda. and, therefore, they become more attractive at longer wavelengths than electrooptic modulators where the drive power increases in accordance with .lambda..sup.3.
One type of prior art magneto-optic bounce-cavity type modulator that could be used is disclosed in U.S. Pat. No. 3,420,601 to R. W. Young et al issued Jan. 7, 1969. In this type of modulator a polarized input beam is reflected by two mirrors that are formed on opposite surfaces of a magneto-optic crystal. An electrical coil surrounding the crystals permits a current in the coil to determine whether or not the polarization of the input beam will be changed in passing through the crystal. An output polarization analyzer is placed in the path of the output beam and oriented so as to couple only the polarization that corresponds to an unmodified reflected input beam. As a result, changes in the coil current can modulate the intensity of the beam that appears at the output of the polarization analyzer.